Hydraulic suspension for vehicle and multi-functional proportional control valve for the same

ABSTRACT

A hydraulic suspension system includes a suspension cylinder, a pump, and a control valve therebetween. The control valve includes a spool reciprocally movable between a pump flow position and a tank flow position in which a control port of the control valve is in communication with a pump and a tank, respectively. A piloted logic element in fluid communication with and interposed between the control valve and the suspension cylinder is selectively movable between a through-flow position in which fluid can flow in either direction between a chamber of the suspension cylinder and the control port of the control valve and a blocked position in which fluid is prevented from flowing in or out of the chamber of the suspension cylinder. The logic element is biased to the blocking position, moving to the through-flow position when subjected to a crack pressure delivered from the control port of the control valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of priority to U.S.Provisional Patent Application No. 61/776,505, filed on Mar. 11, 2013,and entitled “Hydraulic Suspension System for Vehicles andMulti-Functional Proportional Control Valve for the Same,” which isincorporated in its entirety herein by this reference.

TECHNICAL FIELD

This patent disclosure relates generally to a hydraulic suspensionsystem and, more particularly, to a hydraulic suspension system, (e.g.,axle suspension, single wheel suspension, cabin suspension) where acombination of valves is used to control the suspension cylinder(s) tothe nominal position when the load on the system has changed or tocharge or discharge the rod side pressure in a double-acting system tothereby adjust the spring curve.

BACKGROUND

In conventional commercial systems, at least two solenoid valves areused to control a single-acting cylinder, and at least three solenoidvalves (see, e.g., U.S. Pat. No. 8,096,568 B2 to Huth) or four solenoidvalves (see, e.g., U.S. Patent Application Publication No.US2005/0050886 A1 to Bauer et al.) are used to control a double-actingsystem independently at the same time. In other known systems, threesolenoid valves in combination with one proportional pressure-reducingvalve are used to control a double-acting system independently at thesame time (see, e.g., U.S. Pat. No. 7,219,779 B2 to Wolfgang and U.S.Pat. No. 7,048,280 B2 to Brandenburger). Another known system uses twoproportional and two solenoid valves to control a double-acting systemindependently (see, e.g., U.S. Pat. No. 7,753,385 B2 to Bitter).

Some existing systems are equipped with additional, non-integral checkvalves for load sensing/piloting. Additionally, check valves orlow-leakage solenoid-operated valves are included in some conventionalsystems to hold the mechanical system rigid when power is not applied.

It will be appreciated that this background description has been createdby the inventors to aid the reader, and is not to be taken as anindication that any of the indicated problems were themselvesappreciated in the art. While the described principles can, in someaspects and embodiments, alleviate the problems inherent in othersystems, it will be appreciated that the scope of the protectedinnovation is defined by the attached claims, and not by the ability ofany disclosed feature to solve any specific problem noted herein.

SUMMARY OF THE DISCLOSURE

The present disclosure, in one aspect, is directed to embodiments of ahydraulic circuit configured to reduce the complexity and cost of thecombination of valves used in a suspension system while maintainingequivalent or improved performance compared to existing solutions. Inaddition, the present disclosure, in another aspect, is directed toembodiments of a multi-function control valve adapted for use withembodiments of a hydraulic circuit where a single-acting cylinder can becontrolled (extended and retracted) with only one control valve. Inanother aspect, embodiments of a multi-function control valve areincluded in a hydraulic circuit in which only two control valves areneeded to allow independent control from the piston and rod side(extended and retracted or charging and discharging) of a double-actingsystem.

In one embodiment, a hydraulic suspension system includes a controller,a pump, a tank, a suspension cylinder, a proportionalpressure-reducing/-relief control valve, and a logic element. The pumpis adapted to provide a source of pressurized fluid, and the tank isadapted to hold a reservoir of fluid. The tank is in fluid communicationwith the pump. The suspension cylinder is in selective fluidcommunication with the pump. The suspension cylinder defines a chambertherein adapted to receive pressurized fluid.

The proportional pressure-reducing/-relief control valve is inelectrical communication with the controller and in fluid communicationwith the pump. The control valve includes a spool reciprocally movableover a range of travel between at least a pump flow position in whichthe pump and a control port of the control valve are in fluidcommunication with each other and a tank flow position in which the tankand the control port of the control valve are in fluid communicationwith each other. The control valve is adapted such that the spool movesin response to a control signal received from the controller and thefluid pressure at the control port.

The logic element is in fluid communication with and interposed betweenthe control valve and the suspension cylinder. The logic elementincludes a poppet selectively movable between a through-flow position inwhich fluid can flow in either direction between the chamber of thesuspension cylinder and the control port of the control valve and ablocked position in which fluid is prevented from flowing out of thechamber of the suspension cylinder. The logic element is biased to theblocking position. The logic element is adapted to move from theblocking position to the through-flow position when a pressure at afluid region upstream of the logic element poppet exceeds apredetermined crack pressure. The fluid region upstream of the logicelement poppet is in fluid communication with the control port of thecontrol valve.

In another aspect of the present disclosure, a multifunctionalproportional control valve includes a control valve portion and a logicelement portion in communication with the control valve portion. Thecontrol valve portion and the logic element portion are contained withina single cartridge arrangement.

The control valve portion includes a control valve cage and a hollowspool. The control valve cage defines a longitudinal interiorpassageway, a tank port, and a pump port. The tank and pump ports are incommunication with the interior passageway. The spool defines alongitudinal spool passageway and a plurality of cross holes radiallyarranged about the spool. The cross holes are in communication with thespool passageway and the interior passageway of the control valve cage.The spool is disposed within the interior passageway of the controlvalve cage and reciprocally movable over a range of travel between apump flow position in which the pump port of the control valve cage isopen and the tank port of the control valve cage is closed and a tankflow position in which the tank port of the control valve cage is openand the pump port of the control valve cage is closed. The spool isbiased to the pump flow position.

The logic element portion includes a logic element cage and a logicelement poppet. The logic element cage defines a longitudinal interiorlogic element passageway and a logic element port in communication withthe logic element passageway. The logic element passageway is incommunication with the spool passageway. The logic element poppet isdisposed within the logic element passageway of the logic element cageand is reciprocally movable over a range of travel between a blockingposition in which the logic element port of the logic element cage isclosed and a logic element through-flow position in which the logicelement port of the logic element cage is open. The logic element poppetis biased to the blocking position such that the logic element poppetremains in the blocking position until a pressure at least equal to acrack pressure is applied to the logic element poppet against thebiasing force, thereby unseating the logic element poppet from theblocking position and moving the logic element poppet toward thethrough-flow position.

Further and alternative aspects and features of the disclosed principleswill be appreciated from the following detailed description and theaccompanying drawings. As will be appreciated, the hydraulic circuits,the multi-function control valves, and methods disclosed herein arecapable of being carried out in other and different embodiments, andcapable of being modified in various respects. Accordingly, it is to beunderstood that both the foregoing general description and the followingdetailed description are exemplary and explanatory only and do notrestrict the scope of the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of a hydraulic circuit.

FIG. 2 is a schematic view of an embodiment of a hydraulic circuit inaccordance with principles of the present disclosure, illustrating asingle-acting system.

FIG. 3 is a graph of an illustrative controller digital voltage output(U) and corresponding current (I) to control valve versus time (t) for asingle-acting system in accordance with principles of the presentdisclosure, illustrating a controller output in a condition referred toas “on-high.”

FIG. 4 is a graph of another illustrative controller digital voltageoutput (U) and corresponding current (I) to control valve versus time(t) for a single-acting system in accordance with principles of thepresent disclosure, illustrating a controller output in a conditionreferred to as “on-low.”

FIG. 5 is a graph of illustrative valve settings versus time for asingle-acting system in accordance with principles of the presentdisclosure, illustrating the control pressure between a proportionalpressure-reducing/-relieving valve and a logic element valve, thepressure in a cylinder, and the current to the proportionalpressure-reducing/-relieving valve over time.

FIG. 6 is a schematic view of an embodiment of a hydraulic circuit inaccordance with principles of the present disclosure, illustrating asingle-acting system with a constant pump.

FIG. 7 is a schematic view of another embodiment of a hydraulic circuitin accordance with principles of the present disclosure, illustrating asingle-acting system with a one-way restriction orifice.

FIG. 8 is a schematic view of an embodiment of a hydraulic circuit inaccordance with principles of the present disclosure, illustrating adouble-acting system.

FIG. 9 is a schematic view of an embodiment of a hydraulic circuit inaccordance with principles of the present disclosure, illustrating adouble-acting system with a pair of one-way restriction orifices.

FIG. 10 is a schematic view of another embodiment of a hydraulic circuitin accordance with principles of the present disclosure, illustrating adouble-acting system with an embodiment of a multi-functional controlvalve constructed in accordance with principles of the presentdisclosure.

FIG. 11 is an elevational view, in cross section, of an embodiment of amulti-functional control valve constructed in accordance with principlesof the present disclosure.

DETAILED DESCRIPTION

Embodiments of a hydraulic circuit constructed in accordance withprinciples of the present disclosure are adapted to control the positionand/or the pressure of a suspension cylinder (e.g., axle suspension,single wheel suspension, cabin suspension). In embodiments of ahydraulic suspension system, a proportional pressure-reducing/-relievingvalve is adapted to open and close a piloted logic element valve tocontrol the cylinder pressure/position. Embodiments of a hydraulicsuspension circuit constructed in accordance with principles of thepresent disclosure can have the same or similar functionality asconventional circuits, but with reduced complexity.

Embodiments of a control valve constructed in accordance with principlesof the present disclosure combine the functionality of several valvesinto one cartridge that is used to control the suspension cylinders) tothe nominal position/pressure when the load on the system has changed.In embodiments, a control valve constructed in accordance withprinciples of the present disclosure combines the functionality ofmultiple conventional valves in a hydraulic suspension systemconstructed in accordance with principles of the present disclosure intoone valve. In embodiments, a proportional valve in combination with acontrol strategy following principles of the present disclosure reducesthe number of components (e.g., valves, controller outputs, manifoldsize) which are needed to control a suspension system.

Following principles of the present disclosure, embodiments of ahydraulic suspension system can achieve similar functionality asconventional systems but with reduced cost and complexity. Cost can bereduced by reducing the number of components and wire connectionsrelative to prior solutions. For example, in embodiments, the system canbe equipped with a smaller/lower weight manifold relative to one used ina conventional system that will still provide the desired performancecharacteristics.

Embodiments of a hydraulic suspension system according to principles ofthe present disclosure can have improved reliability as a result ofusing a reduced number of valves and wire connections and acorresponding reduced number of controller outputs. For example, inembodiments, only one controller output and one coil are used for asingle-acting system, and only two controller outputs and two coils areused for a double-acting system.

In embodiments, a hydraulic suspension system and a multi-functionalcontrol valve constructed in accordance with principles of the presentdisclosure can provide enhanced system performance in that proportionalcontrol can be provided, rather than simply an on/off condition. Inembodiments, two digital control outputs with a third stage (off,on-low, on-high) can be used to control the hydraulic suspension system.In other embodiments, one digital control output with one proportionaloutput can be provided but without the need for a pressure transducer.In still other embodiments including one digital control output and oneproportional output, pressure on a rod side of the suspension cylindercan be kept constant during the stroke of the piston assembly by using alevel-control feature on the piston side.

In embodiments of a double-acting system following principles of thepresent disclosure, two proportional control outputs can be providedwhich can yield higher performance of the control algorithm (e.g., incombination with uni-directional restrictors or without restrictors).The speed of the level and the pressure control is adjustable.Independent control of the piston side (level control) and the rod side(pressure control) with two independent valves (charge and discharge atthe same time) is possible. The pressure on the rod side can be adjustedto different settings to thereby produce different spring curves. Thisadjustment can be done related to several parameters, such as drivingspeed, axle load, drivers setting, etc. Systems constructed according toprinciples of the present disclosure can be used as an active suspensionsystem (in special situations, for example, during braking or duringacceleration).

In combination with two proportional outputs, the pressure can becontrolled continuously with a multi-functional control valveconstructed according to principles of the present disclosure to adesired value. A multi-functional control valve constructed according toprinciples of the present disclosure can be contained within a singlecartridge available in different sizes to accommodate different flowrequirements. In single-acting systems, embodiments of a valveconstructed in accordance with principles of the present disclosure canbe included into the cylinder bottom without the need for a manifold. Amulti-functional control valve constructed according to principles ofthe present disclosure can be used in a variety of applications,including a suspension system and a single or double-acting hitch, forexample.

Turning now to the Figures, a hydraulic circuit 100 is shown in FIG. 1.A proportional pressure-reducing/-relieving valve 102 can be used tocontrol a single-acting cylinder 104. By increasing or decreasing thecontrol pressure of the pressure-reducing/-relieving valve 102, acylinder rod 106 of the single-acting cylinder 104 can be extracted orretracted. If the pressure setting of the proportional valve 102 is heldconstant, the cylinder rod 106 position stays fixed. A variabledisplacement pump 107 can be adapted to selectively provide a source ofpressurized hydraulic fluid to the cylinder 104 through thepressure-reducing/-relieving valve 102.

In the case of a suspension cylinder, the valve 102, operating alone, iskept permanently energized to hold a position. If the valve 102 werede-energized, the cylinder rod 106 would retract under any load.Constantly energizing the coil 108 of the valve 102 to hold a loadrequires the use of both electric and hydraulic energy, which may beundesirable and pose a safety concern in that the machine behavior maybecome unpredictable should power be lost during operation.

To avoid the need to constantly energize the coil 108 of the valve 102,the circuit 100 of FIG. 1 includes a solenoid-operated,two-way/two-position poppet valve 115. The function of the solenoidpoppet valve 115 in the circuit 100 of FIG. 1 is to work as a load-hold,or position-hold, valve. The position of the cylinder rod 106 can bechanged with the pressure-reducing/-relieving valve 102 with thesolenoid poppet valve 115 being operated at the same time. As soon asthe reference position is reached, the solenoid poppet valve 115 and thepressure-reducing/-relieving valve 102 can be de-energized. The positionof the cylinder rod 106 can be maintained, substantially leakage free,by the solenoid poppet valve 115. An accumulator 120 can be provided toreduce the rate of pressure increase as the cylinder rod 106 strokes. Arelief valve 125 can be provided to protect the cylinder 104 and theaccumulator 120 from excessive pressure spikes.

The circuit 100 of FIG. 1 uses two solenoids 102, 115 to control thesingle-acting cylinder 104. The circuit 100 of FIG. 1, however, canallow for the lowering and lifting speed to be adjusted, depending onthe control current to the proportional pressure-reducing/-relievingvalve 102. If this concept is used with a double-acting system, thepressure in a cylinder rod side 127 of the cylinder 104 can becontrolled with the pressure reducing valve 102 without the need of apressure transducer.

Referring to FIG. 2 an embodiment of a hydraulic circuit 200 constructedin accordance with principles of the present disclosure is shown. Thehydraulic circuit 200 is adapted for a single-acting suspension system.In the hydraulic circuit 200 of FIG. 2, the solenoid-operated twoway/two position poppet valve 115 of the hydraulic circuit 100 of FIG. 1is omitted. The hydraulic circuit 200 includes a piloted logic element215 in operative cooperation with a pressure-reducing/-relieving valve202. The hydraulic circuit 200 of FIG. 2 also includes a suspensioncylinder, a controller or electronic control unit (ECU) 210, a variabledisplacement pump 220, a tank 221, a load-sense check valve 231, anorifice 240, an accumulator 250, a pressure relief valve 255, a pressuresensor 260, and a position sensor 270.

The variable displacement pump 220 is adapted to provide a source ofpressurized fluid, and the tank 221 is adapted to hold a reservoir offluid. The tank 221 is in fluid communication with the pump 220 suchthat the pump 220 can selectively draw fluid from the tank 221 forproviding the source of pressurized fluid. The pump 220 and the tank 221are both in selective fluid communication with the control valve 202. Aload sense line 230 extends between the pump 220 and the piloted logicelement 215. The tank 221 is in selective fluid communication with thepressure relief valve 255.

The suspension cylinder 204 is in selective fluid communication with thepump 220 and the tank 221. The control valve 202, the piloted logicelement 215, and the orifice 240 are interposed between the pump 220 andthe suspension cylinder 204. The control valve 202 and the piloted logicelement 215 are adapted to selectively fluidly connect the suspensioncylinder 204 to the pump 220 and the tank 221. The suspension cylinder204 includes a reciprocally movable cylinder rod 206 and defines achamber 208 therein adapted to receive pressurized fluid.

The pressure sensor 260 can be configured to sense the pressure in thechamber 208 (piston-side) of the cylinder 204. The position sensor 270can be operably arranged with the cylinder rod 206 and adapted to detectthe position of the cylinder rod 206 over its stroke between a retractedposition and an extended position.

The proportional pressure-reducing/-relief control valve 202 is inelectrical communication with the controller 210 and in selective fluidcommunication with the pump 220 and the tank 221. The control valve 202includes a spool 212 reciprocally movable over a range of travel betweenat least a pump flow position in which the pump 220 and a control port211 of the control valve 202 are in fluid communication with each otherand a tank flow position in which the tank 221 and the control port 211of the control valve 202 are in fluid communication with each other. Thecontrol valve 202 is adapted such that the spool 212 moves in responseto a control signal sent to a coil assembly 214 of the control valve 202received from the controller 210. The control valve 202 can include acoil 214 which is adapted to selectively move the spool 212. Inembodiments, the control valve 202 can be biased to the pump flowposition.

The piloted logic element 215 can be adapted to selectively maintain thecylinder rod in its position when the control valve 202 is de-energized.The piloted logic element 215 is in fluid communication with andinterposed between the control valve 202 and the suspension cylinder204. The logic element 215 includes a poppet 217 selectively movablebetween a through-flow position in which fluid can flow in eitherdirection between the chamber 208 of the suspension cylinder 204 and thecontrol port 211 of the control valve 202 and a blocked position inwhich fluid is prevented from flowing out of the chamber 208 of thesuspension cylinder 204 to the control port 211 of the control valve202. In embodiments, the logic element 215 is constructed such thatfluid can flow from the control port 211 of the control valve to thechamber 208 of the suspension cylinder when the poppet 217 is in theblocked position. The illustrated logic element 215 is biased to theblocked position. The logic element 215 includes a pilot port 216 and isadapted to move from the blocking position to the through-flow positionwhen a pressure at the pilot port 216 exceeds a predetermined value,referred to as a “crack” pressure. The pilot port 216 is in fluidcommunication with the control port 211 of the control valve 202.

The load sense line 230 is adapted to provide a load sense signal to thepump 220. The pump 220 is adapted to vary a flow of pressurized fluid inresponse to the load sense signal to generate a desired flow to thecontrol valve 202. The load sense line 230 is in fluid communicationwith the control port 211 of the pressure-reducing/-relieving controlvalve 202, the piloted logic element 215, and the pump 220 through aload sense port 235. The load sense line 230 includes the load-sensecheck valve 231, which is adapted to prevent a flow of fluid from thepump 220 to the control valve 202 or the logic element 215 but to allowa flow of fluid from a pilot junction 232 along the load sense line 230to the pump 220.

In embodiments, the orifice 240 can be disposed between the logicelement 215 and the chamber 208 of the suspension cylinder 204. Theorifice 240 can be adapted to control a rate of flow of pressurizedfluid to and from the chamber 208 of the suspension cylinder 204 toallow additional tuning of the speed at which the cylinder rod 206reciprocally extends and retracts.

The accumulator 250 can be placed in fluid communication with andinterposed between the piloted logic element 215 and the suspensioncylinder 204. In embodiments, the accumulator 250 can be configured toreduce the rate of pressure increase as the cylinder rod 206reciprocally strokes.

The relief valve 255 can be provided to protect the suspensionaccumulator 250 in fluid communication with the suspension cylinder 204and the suspension cylinder 204 itself against high pressure peaks. Therelief valve 255 is in fluid communication with the tank 221 and inparallel fluid relationship with the suspension, cylinder 204, theaccumulator 250, and the piloted logic element 215. The relief valve 255can be adapted such that a pressurized fluid exceeding a predeterminedthreshold is diverted away from the accumulator 250 and the suspensioncylinder 204 to the tank 221.

The ECU 210 can be provided to operate the circuit 200. In embodiments,the ECU 210 can comprise any suitable controller known to those skilledin the art. The controller 210 can be in electrical communication withone or more sensors, such as the pressure sensor 260 and/or the positionsensor 270 to obtain operational information regarding the condition ofthe circuit 200 to help the controller 210 operate. The ECU 210 can beused to selectively provide current to the coil assembly 214 of thecontrol valve 202 based on computer-readable operational logic stored ona non-transitory computer readable medium accessed by the processor ofthe controller 210.

In embodiments, the control valve 202 can be used to control thesingle-acting suspension cylinder 204. By increasing or decreasing thecontrol pressure of the control valve 202, the cylinder rod 206 can beextended or retracted. If the pressure setting of the control valve 202is held constant, the cylinder rod 206 can remain fixed in place.

In embodiments, a hydraulic manifold can be used to control the positionof the suspension cylinder 204. When the load on the cylinder 204changes, the position will change and then the suspension stroke in onedirection will be decreased. Therefore, the ECU 210 can be adapted tocontrol the cylinder 204 back to its nominal position such that it hasthe maximum suspension stroke available. As soon as the control valve202 is operated (e.g., control current to the coil 214 is higher thanthe offset), the valve 202 is controlling a pressure at the pilot port216 of the logic element 215. The logic element 215 opens in response tothe pilot pressure, thereby allowing flow to or from the cylinder 204.Furthermore, a load sense signal is sent through the load-sense checkvalve 230 to the load-sense port 235 of the pump 220 which is adapted togenerate the required pressure/flow.

If the pressure controlled with the pressure-reducing/-relieving controlvalve 202 is lower than the pressure in the chamber 208 of the cylinder204 but higher than the crack pressure of the logic element 215, thelogic element 215 is in the through-flow position and fluid in thechamber 208 of the suspension cylinder 204 drains therefrom, therebyretracting the cylinder rod 206 of the cylinder 204. If the pressurecontrolled with the pressure-reducing-relieving valve 202 is higher thanthe pressure in the cylinder 204 and the crack pressure of the logicelement 215, the logic element 215 is in the through-flow position andfluid flows from the pump 220 to the chamber 208 of the suspensioncylinder 204, thereby extending the cylinder rod 206 of the cylinder204.

As soon as the reference position is reached, the control current forthe coil 214 of the control valve 202 can be set to zero, and the logicelement 215 closes in response to the pilot pressure dropping below thecrack pressure of the logic element 215 such that the poppet 217 movesto the blocked position. With the logic element 215 closed, the positionof the cylinder rod 206 of the cylinder 204 is maintained until the loadchanges.

In one configuration, when the digital controller output of thecontroller 210 is switched off, no current is applied to thepressure-reducing/-relieving control valve 202, and the controlledpressure is lower than the crack pressure setting of the logic element215. The logic element 215 is closed, and there is no load sense signalthrough the load-sense check valve 230 in the load sense line 231 incommunication with the pump 220.

An operative condition referred to as “on-high” is shown in FIG. 3. Whenthe output of the digital controller 210 is switched to an operativecondition referred to as “on-high,” the maximum current is applied tothe solenoid assembly 214 of the pressure-reducing/-relieving controlvalve 202, resulting in the maximum pressure setting of the controlvalve 202 at the control port. A fluid region upstream of the logicelement 215 relative to the suspension cylinder 204 (in the illustratedembodiment, the pilot port 216) is in fluid communication with thecontrol port 211 of the control valve 202, and the poppet 217 of thelogic element 215 moves to the through-flow position when the pressureat the fluid region upstream of the logic element 215 exceeds apredetermined crack pressure.

The load sense signal sensed at the control port 211 of thepressure-reducing/-relieving control valve 202 causes the pump 220 toincrease the supply pressure to the pressure-reducing/-relieving controlvalve 202 to meet the pressure requirements of the load. As fluid flowsfrom the control port 211 of the pressure-reducing/-relieving controlvalve 202 and through the logic element 215, the cylinder rod 206 willextend. In embodiments, the position sensor 270 can be used to detectthe position of the cylinder rod 206, and/or the pressure sensor 260 canbe used to detect the pressure in the piston-side of the suspensioncylinder 204 (the chamber 208). The position signal and/or the pressuresignal generated by the respective sensor 270, 260 can be sent to theECU 210 which is adapted to use the signal(s) to control the operationof the control vale 202 and/or the pump 220.

When the reference position or pressure is reached, the digitalcontroller output of the ECU 210 is switched off again. This causes thepressure at the control port 211 of the proportionalpressure-reducing/-relieving control valve 202 to drop below the crackpressure of the logic element 215. The logic element 215 closes (thepoppet 217 moves back to the blocking position) and holds the pressurein the piston-side of the cylinder 204.

To retract the position of the cylinder rod 206 or to reduce thepressure in the piston-side of the cylinder 204, the digital controlleroutput of the ECU 210 can be switched to a condition called “On-low,” asshown in FIG. 4. The graph in FIG. 4 illustrates the controller outputswitching between on and off states in a defined cycle time. Due to theinductance of the coil circuit, the current which is applied to thecontrol valve 202 oscillates at about 30% percent of the maximumcurrent, which would have been reached if the output is permanentlyswitched on (see FIG. 3).

The ECU 210 can be adjusted to selectively turn the digital controlleroutput on and off for a predetermined cycle time. For example, in onearrangement, the ECU 210 can vary the cycle time such that the outputcan be alternately switched on for x cycles, then switched off for 2xcycles, then switched on for x cycles, switched off for 2x cycles and soon, thereby creating a pseudo pulse-width modulation (PWM) controlcurrent. In some embodiments, x can be equal to about 1, but other timeratios can be used in other embodiments.

The current applied to the coil 214 of the pressure-reducing/-relievingcontrol valve 202 to retract the cylinder rod 206 of the cylinder 204 orlower the piston-side pressure of the cylinder 204 is shown in FIG. 4.With a low current applied to the pressure-reducing/-relieving valve202, the pressure sensed by the logic element 215 is slightly higherthan the crack pressure which is required to open the logic element 215.The logic element 215 will open. Since the pressure in the piston-sideof the cylinder 204 is higher than the pressure controlled with thepressure-reducing/-relieving control valve 202, the hydraulic oil willflow from the cylinder 204 through the orifice 240, through the logicelement 215, and through the pressure-reducing/-relieving control valve202 in relieving mode to the tank 221. This flow of hydraulic oil fromthe cylinder 204 to the tank 221 will continue as long as the controlleroutput is in this described “On-low” state or until the pressure in thecylinder 204 reaches the pressure setting of the proportionalpressure-reducing/-relieving control valve 202.

Referring to FIG. 5, an example of the control pressure, cylinderpressure, and proportional pressure-reducing/-relieving control valvecurrent over time for a single-acting system similar to the circuit 200of FIG. 2 is shown. P1 is the control pressure between the proportionalpressure-reducing/-relieving control valve 202 and the logic element215. P4 is the pressure of the cylinder 204. I is the current to thecoil 214 of the proportional pressure-reducing/-relieving control valve202.

Referring to FIG. 6, another embodiment of a hydraulic circuit 300 for asingle-acting system constructed in accordance with principles of thepresent disclosure is shown. The hydraulic circuit 300 includes apressure-reducing/-relieving control valve 302, a suspension cylinder304, a controller 310, a piloted logic element 315, a constant flow pump320, a tank 321, an orifice 340, an accumulator 350, a pressure reliefvalve 355, a pressure sensor 360, and a position sensor 370.

The piloted logic element 315 is in operative cooperation with thepressure-reducing/-relieving valve 302. The proportionalpressure-reducing/-relief control valve 302 is in electricalcommunication with the controller 310 and in selective fluidcommunication with the pump 320. The logic element 315 is in fluidcommunication with and interposed between the control valve 302 and thesuspension cylinder 304. These components can operate as explained aboveto control the cylinder 304.

The constant flow pump 320 is adapted to provide a constant flow ofpressurized fluid. In thus case, the circuit 300 does not include theload sense function or the hydraulic load sense line 230 including thecheck valve 231 as is shown in the hydraulic circuit 200 of FIG. 2. Toimprove hydraulic efficiency, the circuit 300 of FIG. 6 can include asolenoid relief valve 305 or an unloading pressure compensatorinterposed between the constant flow pump 320 and the control valve 302.The solenoid relief valve 305 can be in electrical communication withthe controller 310 such that the ECU 310 can be used to control itsoperation. The construction and functionality of the hydraulic circuit300 of FIG. 6 can be similar in other respects to the hydraulic circuit200 of FIG. 2.

Referring to FIG. 7, another embodiment of a hydraulic circuit 400 for asingle-acting system constructed in accordance with principles of thepresent disclosure is shown. The hydraulic circuit 400 includes apressure-reducing/-relieving valve 402, a suspension cylinder 404, acontroller 410, a piloted logic element 415, a variable displacementpump 420 with a load sense line 430, a tank 421, an accumulator 450, apressure relief valve 455, a pressure sensor 460, and a position sensor470.

The piloted logic element 415 is in operative cooperation with thepressure-reducing/-relieving valve 402. The proportionalpressure-reducing/-relief control valve 402 is in electricalcommunication with the controller 410 and in selective fluidcommunication with the pump 420. The logic element 415 is in fluidcommunication with and interposed between the control valve 402 and thesuspension cylinder 404. These components can operate as explained aboveto control the cylinder 404.

The circuit 400 of FIG. 7 includes a one-way restrictor 441 rather thanan orifice 240 as found in the hydraulic circuit 200 of FIG. 2. Theone-way restrictor 441 is disposed between the logic element 415 and thechamber 408 of the suspension cylinder 404. In embodiments, the one-wayrestrictor 441 is adapted to control a rate of flow of pressurized fluidin one direction between the piloted logic element 415 and the cylinder404, either to or from the chamber 408 of the suspension cylinder 404.

In the illustrated embodiment, the one-way restrictor 441 does notrestrict the flow of fluid from the piloted logic element 415 to thecylinder 404, but restricts the flow of fluid from the cylinder 404 tothe piloted logic element 415. By using the one-way restrictor 441 asshown, the cylinder rod 406 of the suspension cylinder 404 can beextended very quickly while providing a slow controlled retraction(alternatively, the cylinder rod 406 could be retracted very quicklywhile providing slow, controlled extension using a one-way restrictorarranged in the opposite fashion). This can be beneficial in specialsituations involving front-axle suspension systems. The construction andfunction of the hydraulic circuit 400 of FIG. 7 can be similar in otherrespects to the hydraulic circuit 200 of FIG. 2.

Referring to FIG. 8, an embodiment of a hydraulic circuit 500constructed in accordance with principles of the present disclosure fora double-acting suspension system is shown. The hydraulic circuit 500 ofFIG. 8 includes a piston-side pressure-reducing/-relieving control valve502, a rod-side pressure-reducing/-relieving control valve 503, asuspension cylinder 504, a controller 510, a pair of piloted logicelements 515, 516, a variable displacement pump 520 with a load senseline 530, a tank 521, a piston-side orifice 540, a rod-side orifice 541,a piston-side accumulator 550, a rod-side accumulator 551, a pressurerelief valve 555, a piston-side pressure sensor 560, a rod-side pressuresensor 561, and a position sensor 570.

The double-acting suspension system 500 uses a piston side 526 and a rodside 527 of a chamber 508 of the suspension cylinder 504 for thesuspension function. The suspension cylinder 504 includes a body 505 anda piston assembly 507 disposed within the body 505 that is reciprocallymovable over a range of travel between a retracted position and anextended position. The piston assembly 507 includes a piston 509 and arod 506, at least a portion of which extends from the body 505. The body505 defines the piston-side chamber 526 and the rod-side chamber 527.

The load sense pump 520 can be adapted to provide a source ofpressurized hydraulic fluid to both the piston-sidepressure-reducing/-relieving control valve 502 and the rod-sidepressure-reducing/-relieving control valve 503, which are all inelectrical communication with the ECU 510. The control valves 502, 503are each in turn associated with the piloted logic elements 515, 516,the orifices 540, 541, and the accumulators 550, 551, respectively.

The load sense line 530 fluidly connects the control port 511 of thepiston-side pressure-reducing/-relieving control valve 502 and itsassociated piloted logic element 515 with the pump 520 through aresolver 531. The load sense line 530 also fluidly connects the controlport 511 of the rod-side pressure-reducing/-relieving control valve 503and its associated piloted logic element 516 with the pump 520 throughthe resolver 531. The load sense line 530 is adapted to provide a loadsense signal to the pump 520 through a load sense port 535. The pump 520is adapted to vary a flow of pressurized fluid in response to the loadsense signal to generate a desired flow to the control valve 202.

The pair of orifices 540, 541 is respectively disposed between thepiston-side logic element 515 and the cylinder 504 and between therod-side logic element 516 and the cylinder 504. Both sides 526, 527 ofthe cylinder chamber 508 are independently connected to the respectiveaccumulators 550, 551. The position control of the cylinder rod 506 canbe performed by increasing or decreasing the oil volume in the pistonside 526 of the cylinder 504. The rod side 527 of the cylinder 504 canbe pressurized with a constant or variable pressure. The illustratedcircuit 500 of FIG. 8 provides a variable rod side pressure with thedisclosed circuit concept.

The function of the circuit 500 of FIG. 8 is similar to the singleacting suspension circuit 200 of FIG. 2. The position control (cylinderpiston side 526) works in a manner similar to that described above inconnection with a single-acting system, such as in FIG. 2. For thepressure control in the cylinder rod side 527, several scenarios arepossible. The pressure in the cylinder rod side 527 can be controlled byusing the rod-side pressure sensor 561 to detect the pressure in the rodside 527 of the cylinder 504. The rod-side proportionalpressure-reducing/-relieving control valve 503 can be operated using aclosed control loop with a feedback or feed-forward control loop such asa PID-controller or equivalent algorithm to control the pressure to thereference value. The pressure in the cylinder rod side 527 can beincreased and decreased in a similar manner as the position of thecylinder rod 506 is controlled. If the pressure controlled with therod-side proportional pressure-reducing/-relieving control valve 503 islower than the pressure in the rod side 527 of the cylinder 504 buthigher than the crack pressure of the rod-side logic element 516, thepressure in the rod side 527 of the cylinder 504 will be reduced. If thepressure controlled with the rod-side proportionalpressure-reducing/-relieving control valve 503 is higher than thepressure in the rod-side 527 of the cylinder 504, the pressure in therod side 527 of the cylinder 504 will be increased.

A second option to control the pressure in the cylinder rod side 527 isto set the current to the rod-side proportionalpressure-reducing/-relieving control valve 503 to regulate a desiredpressure according to the characteristic curve of the control valve 503during cylinder piston side 526 adjustments. One way this can beaccomplished is by using the ECU 510 with a PWM-output with currentfeedback to control the current to the rod-side proportionalpressure-reducing/-relieving control valve 503.

A third option (also used for position control) to control the pressurein the cylinder rod side 527 is to use the rod-side proportionalpressure-reducing/-relieving control valve 503 controlled by a digitaloutput from the controller 510 to provide no output, “on-low”, or“on-high” current to the control valve as previously described above. Adouble-acting system can be configured to replicate this control schemeto control the piston-side pressure-reducing/-relieving control valve502 and the rod-side proportional pressure-reducing/-relieving controlvalve 503. This method is beneficial, since all ECU's may not have freePWM outputs available. The rod-side pressure sensor 561 can be used todetect if the pressure in the rod-side 527 of the cylinder 504 shoulddecrease, increase, or if it is in the acceptable range. The pressure isthen adjusted using either an “on-low” current or “on-high” current ormaintained with no current to the valve. The discussion of the operationof the circuit 200 of FIG. 2 is referred to for further details, whichare applicable to the operation of the rod-side 527 of the circuit 500of FIG. 8, as well. In a double-acting system, the rod and piston side527, 526 of the cylinder 504 can be controlled independently andconcurrently.

Referring to FIG. 9, another embodiment of a hydraulic circuit 600constructed in accordance with principles of the present disclosure isshown, which is a double-acting system similar to the circuit 500 ofFIG. 8. The hydraulic circuit 600 of FIG. 9 includes a piston-sidepressure-reducing/-relieving control valve 602, a rod-sidepressure-reducing/-relieving control valve 603, a suspension cylinder604, a controller 610, a piston-side piloted logic elements 615, apiston-side piloted logic element 616, a variable displacement pump 620with a load sense line 630, a tank 621, a piston-side accumulator 650, arod-side accumulator 651, a pressure relief valve 655, a piston-sidepressure sensor 560, a rod-side pressure sensor 561, and a positionsensor 570.

The circuit 600 of FIG. 9 is the same as the circuit 500 of FIG. 8except that the piston-side orifice 540 and the rod-side orifice 541 ofthe circuit 500 of FIG. 8 are replaced with a pair of one-way restrictorvalves 642, 643, respectively. The orifice elements of the one-wayrestrictor valves 642, 643 can have a different size from each other insome embodiments.

Referring to FIG. 10, another embodiment of a hydraulic circuit 700constructed in accordance with principles of the present disclosure isshown, which is similar to the circuit 500 of FIG. 8. The hydrauliccircuit 700 comprises a double-acting suspension system which uses apiston side 726 and a rod side 727 of the chamber 708 of a suspensioncylinder 704 for the suspension function. The hydraulic circuit 700 ofFIG. 10 includes a piston-side multifunctional cartridge control valve705, a rod-side multifunctional cartridge control valve 706, thesuspension cylinder 704, a controller 710, a variable displacement pump720 with a load sense line 730, a tank 721, a piston-side orifice 740, arod-side orifice 741, a piston-side accumulator 750, a rod-sideaccumulator 751, a piston-side pressure sensor 760, and a rod-sidepressure sensor 761.

To obtain a space-saving option, the pair of multifunctional cartridgecontrol valves 705, 706 can be provided, which each integrate aproportional pressure-reducing/-relieving control valve 702, a pilotedlogic element 715, and a check valve 712 that perform the same functionas the corresponding components of the circuit 500 of FIG. 8. Forexample, the integrated components of the piston-side multifunctionalcartridge control valve 705 correspond to the piston-sidepressure-reducing/-relieving valve 502, the piston-side logic element515, and the portion of the resolver 531 in the load sense line 530configured to provide a load sense signal for the piston-side of thecylinder 504. In embodiments, the orifices 740, 741 can be integratedinto each of the multifunctional cartridge control valves 705, 706,respectively.

The variable displacement pump 720 is adapted to provide a source ofpressurized fluid, and the tank 721 is adapted to hold a reservoir offluid. The tank 721 is in fluid communication with the pump 720. Theload sense pump 720 can be adapted to provide a source of pressurizedhydraulic fluid to both a piston-side multifunctional cartridge controlvalves 705 and a rod-side multi-functional cartridge control valves 705,which are all in electrical communication with an ECU 710.

The suspension cylinder 704 is in selective fluid communication with thepump 720 via the piston-side multifunctional cartridge control valve 705and the rod-side multifunctional cartridge control valve 706. Thesuspension cylinder 704 defines a chamber 708 therein adapted to receivepressurized fluid. The piston-side 726 and the rod-side 727 of thecylinder chamber 708 are independently connected to the piston-side androd-side accumulators 750, 751 and pressure sensors 760, 761,respectively. The pressure sensors 760, 761 can be disposed between theorifices 740, 741, respectively, and the cylinder 704.

In the circuit 700 of FIG. 10, a load sense check valve 780 can beplaced in a common branch 782 of the load sense line 730. The load sensecheck valve 780 can help to completely unload the load sense pump 720below the residual pressure of the pressure reducing portion of themultifunctional cartridge control valves 705, 706.

Referring to FIG. 11, an embodiment of a multi-functional cartridgevalve 800 constructed in accordance with principles of the presentdisclosure is shown. The illustrated valve 800 includes a control valveportion, a logic element portion, and a load sense portion containedwithin a single cartridge arrangement. In embodiments, the cartridgevalve 800 can be housed within a suitably configured valve body.

In the illustrated valve 800, an electro-magnetic actuator assembly inthe form of a solenoid assembly 850 includes a coil 855, a tube 819, amovable plunger or armature 831, and a pole piece 843. The solenoid 850has a proportional characteristic of magnetic (attractive) force betweenthe pole piece 843 and the plunger 831 which is proportional to thecurrent applied to the coil 855. The tube 819 can comprise a bi-metallicassembly consisting of magnetically attractive and non-attractivematerials. The geometry of the magnetically attractive andnon-attractive materials can be configured to determine the magneticforce characteristic of the solenoid 850. A non-magnetic washer 828between the pole piece 843 and the plunger 831 prevents the plunger 831from latching to the pole piece 843 via residual magnetism.

A pilot spring 829 transmits the solenoid force to a pilot poppet 827.The equilibrium position of the plunger 831 at a given coil current isdetermined when the magnetic force balances with the force of the pilotspring 829. An adjusting screw 830 sets the position of the plunger 831with no current applied to the coil. Turning the adjusting screw 830 inand out of the plunger 831 allows the user to set the desired pressuresetting of the valve at a give current.

A threaded plug 832 at the top of the tube 819 can be removed to allowadjustment of the adjusting screw 830 to provide a pressure setting withno current applied to the coil 855. A spring ring 833 can be provided toretain the plug 832 after the valve 800 is set to the desired pressuresetting and helps prevents unintended removal of the plug 832. Aproximal outer area between the plug 832 and the tube 819 may also befilled with epoxy for further tamper-proof protection, in which case thethreaded plug 832 can be adjusted by the manufacturer and then encasedwith an epoxy. An O-ring 841 and a back-up ring 842 can provided to forma seal between the tube 819 and the plug 832 to help prevent externalleakage. A distal portion 860 of the tube 819 includes a threadedexternal surface 862 adapted to threadingly engage the cavity of a valvebody (not shown).

The valve 800 defines five fluid connection ports (Ports A-E) whichcorrespond to those shown for the multifunctional cartridge controlvalves 705, 706 of the hydraulic circuit 700 of FIG. 10. Port A isdisposed along a longitudinal axis of the valve 800 on the distal faceend 880 of a logic element cage 814. Ports B-E are located along theouter periphery of the valve housing with fluid connections in theradial direction. The Ports E, D, C, B, A are separated from adjacentPorts by an O-ring 837, 834, 812, 811 and an associated pair of back-uprings 836, 835, 805, 804, respectively, to prevent fluid from leakingfrom one port to another. In other embodiments, the Ports E, D, C, B, Amay be separated by a single molded seal.

The logic element cage 814 defines Ports A and B. A logic element seat818 defines Port C. A pressure-reducing/-relieving control valve cage820 defines Ports E and D. An O-ring 840 prevents external leakageproximally from Port E.

A control valve portion can include the control valve cage 820 and ahollow spool 821. The control valve cage 820 defines a longitudinalinterior passageway 910, a tank port E, and a pump port D. The tank andpump ports E, D are in communication with the interior passageway 910 ofthe control valve cage 820. The spool 821 defines a longitudinal spoolpassageway 912 and a plurality of cross holes 914 radially arrangedabout the spool 821. The cross holes 914 of the spool 821 are incommunication with the spool passageway 912 and the interior passageway910 of the control valve cage 820. The spool 821 is disposed within theinterior passageway 910 of the control valve cage 820 and reciprocallymovable over a range of travel between a pump flow position in which thepump port D of the control valve cage 820 is open and the tank port E ofthe control valve cage 820 is closed and a tank flow position in whichthe tank port E of the control valve cage 820 is open and the pump portD of the control valve cage 820 is closed. The spool 821 is biased tothe pump flow position.

The control valve cage 820 has a “floating” connection with the tube 819through an oval spring ring 824 that retains the valve cage 820 to thetube 819 when the valve 800 is removed from the cavity of a valve body.The spring ring 824 is trapped in a machined groove 864 provided on theouter diameter of the cage 820 and a corresponding groove 866 on theinner diameter of the rube 819. When the valve 800 is installed in thecavity of a valve body, the “floating” portion of the valve 800 istrapped between the distal face end 870 of the tube 819 and a shoulder872 of the control valve cage 820 at a proximal outer end of the cavityof the valve body and a distal bottom of the cavity and a distal faceend 880 of the logic element cage 814 at the distal bottom of thecavity.

The reciprocally-movable spool 821 is disposed within the control valvecage 820 and is adapted to selectively open and close the flow area atPort D and Port E. A filter core 822 is installed in the spool 821. Thefilter core 822 is interposed between the radial cross holes 914 of thespool 821 and the orifice 825 of the pilot poppet assembly. The filtercore 822 incorporates an orifice hole and restricts the size of particlethat can pass between the filter core 822 and the spool 821 beforereaching the orifice hole. In embodiments, the filter core 822 can beretained within the spool 821 by a swaging operation that flares anupper lip of the filter core 822 after it is inserted into the spool821.

A spool bias spring 844 can be provided that is adapted to bias thespool 821 to a position in which the spool 821 occludes Port E. A distalend 882 of the spool bias spring 844 is installed in a blind hole 884 ata proximal end 885 of the spool 821 to urge the spool 821 in a distaldirection along the longitudinal axis to a position that closes off PortE (as shown) when the pressure proximally above and distally below thespool 821 is balanced. A spring ring 823, which is installed in a grooveat the proximal end 885 of the spool 821, provides a positive stop inthe distal direction for the spool 821 when it contacts an angledsurface 887 defined between a proximal bore 888 of the cage 820 having afirst diameter and a distal bore 889 of the control valve cage 820having a second diameter which is smaller than the diameter of theproximal bore 888. An O-ring 838 and an associated back-up ring 839 helpseal the spool bias spring chamber 893 from Port E.

In embodiments, the electro-magnetic actuator has a pilot poppetassembly that includes the pilot poppet 827, the pilot spring 829interposed between the armature 831 and the pilot poppet 827, a seat 826retained within the pole piece 843 and defining a longitudinal bore 930therethrough, and an orifice 825 interposed between the longitudinalbore 930 and the spool bias spring 844. The orifice 825 is incommunication with the spool passageway 912. The pilot spring 829 urgesthe pilot poppet 827 into sealing engagement with the seat 826 such thatthe longitudinal bore 930 is occluded until a poppet lifting force isapplied in a direction from the orifice toward the pilot spring 829.

A proximal end 891 of the spool bias spring 844 rests against theorifice disc 825 located within the pole piece 843. The orifice disc 825is engaged with the hardened seat 826. The seat 826 is secured via aninterference fit between the seat 826 and the pole piece 843. The seat826 is further retained from moving proximally by an angled surface,created by the change in diameter, at the proximal end of the seat 826,which makes positive contact with a slight change in diameter of a boreof the pole piece 843. The pilot poppet 827 is engaged with the seat 826to define a low leakage seal until sufficient pressure is presentdistally below the seat 826 to lift the pilot poppet 827 off the seat826 in a proximal direction against the spring force created by thesolenoid actuator 850 above.

In embodiments, the valve 800 can include a load sense portion incommunication with both the control valve portion and a logic elementportion. The illustrated load sense portion includes the logic elementseat 818 and a load sense check ball 806.

The logic element seat 818 is interposed between the control valve cage820 and a logic element cage 814. The logic element seat 818 defines alongitudinal load sense passageway 920 therethrough and a load senseport C, which is in communication with the load sense passageway 920.The load sense passageway 920 is in communication with the spoolpassageway 912 of the control valve portion and a logic element poppet817.

The logic element seat 818 has an interference fit with the pressurereducing/relieving control valve cage 820, which is proximally above thelogic element seat 818, and the logic element cage 814, which isdistally below the logic element seat 818. In other embodiments, thelogic element seat 818 can be connected to the two cages 814, 820 via athreaded connection or other mechanical device such as a spring pin orspring ring (not shown).

The logic element seat 818 defines Port C which comprises a load senseport adapted to actuate a load sense pump or other pump control device,and incorporates a reverse-flow check ball 806. The check ball 806 sitsagainst a seat 892 in the radial passage defined in the logic elementseat 818 and blocks the flow of hydraulic fluid when the pressure atPort C is higher than the internal valve pressure between the spool 821and a logic element poppet 817. A spring ring 808, which is installed ina machined groove 895 in the seat 818, holds the check ball 806 inplace. A roll pin 802 is inserted into a blind hole 896 in the seat 818about one hundred eighty degrees away from the check ball seat to fixthe rotational position of the spring ring 808.

In embodiments, the valve 800 includes a logic element portion which isin communication with the control valve portion. The illustrated logicelement portion includes the logic element cage 814 and the logicelement poppet 817. The logic element cage 814 defines a longitudinalinterior logic element passageway 925 and a logic element port B, whichis in communication with the logic element passageway 925. The logicelement passageway 925 is in communication with the spool passageway912.

The logic element poppet 817 is disposed within the logic elementpassageway 925 of the logic element cage 814 and reciprocally movableover a range of travel between a blocking position in which the logicelement port B of the logic element cage 814 is closed and a logicelement through-flow position in which the logic element port B of thelogic element cage 814 is open. The logic element poppet 817 is biasedto the blocking position such that the logic element poppet 817 remainsin the blocking position until a pressure at least equal to a crackpressure is applied to the logic element poppet 817 against the biasingforce, thereby unseating the logic element poppet 817 from the blockingposition and moving the logic element poppet 817 toward the through-flowposition.

The logic element poppet 817 is engaged with the logic element seat 818via the force of a logic element spring 816. When the pressure betweenthe control valve spool 821 and the logic element poppet 817 causes theforce that acts to open the logic element poppet 817 to exceed the forceof the logic element spring 816 that acts to close the logic elementpoppet 817, the logic element poppet 817 lifts off the logic elementseat 818, thereby allowing flow to Port B defined by the logic elementcage 814. The diameter of the logic element seat 818 matches the borediameter of the poppet 817 so that pressure at Port B will not act toopen the logic element poppet 817.

The second port A can be in fluid isolation with respect to the logicelement port B of the logic element cage 814. In the illustratedembodiment, Port B is internally sealed off from Port A by an O-ring 810and a piston seal 801 on an external surface of the logic element poppet817. The piston seal 801 provides a running seal between the logicelement poppet 817 and the logic element passageway 925 of the logicelement cage 814.

A washer 813 mounted to the logic element poppet 817 provides a seat fora proximal end of the logic element spring 816 which provides a biasforce on the logic element poppet 817. A spring guide 815 supports theopposing distal end of the spring 816, provides guidance for the logicelement spring 816, and hydraulic fluid communication of the logicelement spring chamber 898 to Port A. The spring guide 815 defines apassageway 940 therethrough. In the illustrated embodiment, thepassageway 940 of the spring guide has a longitudinal segment and aplurality of radial segments in communication with the longitudinalsegment. The passageway 940 of the spring guide 815 is in communicationwith the logic element passageway 925 and the second port A of the logicelement cage 814. The illustrated spring guide 815 is retained by aspring ring 807. The spring ring 807 is installed in a machined groove899 in the logic element cage 814. In embodiments, Port A is connectedto tank, or in yet other embodiments can be connected to a pilot signalif the application required the logic element pressure setting to bevariable.

In embodiments of using a multi-functional cartridge valve constructedaccording to principles of the present disclosure, hydraulic fluid canbe supplied from a pump to Port D of the valve 800. The control valvespool 821 allows flow from Port D to the internal volume distally belowthe spool 821. Fluid under the spool 821 communicates with the internalvolume above the spool 821 (the spool bias spring chamber 893) throughthe filter core 822. Fluid above the spool 821 communicates with theinternal volume below the pilot poppet 827 through the orifice disc 825.The pressure exerted by the fluid in the internal volume below the pilotpoppet 827 acts to push the pilot poppet 827 up off the seat 826. Whenthe pressure force acting on the pilot poppet 827 exceeds the forceexerted by the pilot spring 829 on the pilot poppet 827, the pilotpoppet 827 unseats and fluid passes between the seat 826 and the pilotpoppet 827, through the communication passage between the pole piece 843and the tube 819, and out a cylindrical hole provided in the tube threadto Port E.

Flow through the area created when the pilot poppet 827 lifts off theseat 826 results in a pressure drop in the volume just distally underthe pilot poppet 827. The difference in pressure between the volumeunder the seat 826, the volume above the control valve spool 821 anddistally below the spool 821 causes flow through the filter core 822 andthe orifice disc 825.

The resulting pressure drop across the filter core orifice causes anunbalanced pressure force on the spool 821. When the net pressure forceacting upon the spool 821 exceeds the downward force of the spool biasspring 844, the spool 821 moves proximally, thereby closing off flowfrom Port D.

The pressure in the volume distally under the spool 821 also acts tounseat the logic element poppet 817 from the seat 818 in the lower logicelement portion of the valve. The logic element poppet 817 is biasedagainst the seat 818 by the force exerted by the logic element spring816 in the lower portion of the valve. The logic element poppet 817blocks the passage of flow between the volume distally under the controlvalve spool 821 and Port B of the valve until the logic element poppet817 is unseated.

With no current applied to the coil 855, the pressure in the volumebelow the spool 821 is less than what is required to unseat the logicelement poppet 817. When current is applied to the coil 855, the plunger831 is attracted to the pole piece 843. This compresses the pilot spring829 and increases the force holding the pilot poppet 827 against theseat 826 resulting in a higher pressure above and below the spool 821before the spool 821 shifts to close off Port D. When the current isincreased enough, the pressure in the volume below the spool 821 exceedsthe crack pressure of the logic element poppet 817 and the logic elementpoppet 817 unseats from the logic element seat 818, thereby allowingflow either to or from Port B.

If the pressure at Port B is lower than the pressure in the volume underthe spool 821, flow will enter the valve 800 from Port D, travel throughthe spool 821, through the flow area created by the logic element seat818 and the logic element poppet 817, and out of Port B. If the pressureat Port B is higher than the pressure under the spool 821, flow willenter the valve 800 from Port B and pass through the area created by thelogic element seat 818 and the logic element poppet 817. This flow willincrease the pressure in the volume under the spool 821, thereby causingthe spool 821 to shift up and close off Port D. With a steady currentmaintained to the coil 855, the pressure above the spool 821 will remainrelatively constant. Additional flow from Port B will cause the spool821 to continue shifting up until Port E is opened. Flow from the volumeunder the spool 821 passes through the spool 821 and out Port E. Flow inor out of Port B will continue until the pressure under the spool 821and at Port B is equalized or until the current at the coil 855 isdropped so that the pressure under the spool 821 is below the crackpressure of the logic element poppet 817. Once the pressure under thespool 821 is below the crack pressure of the logic element poppet 817,the logic element poppet 817 will again reseat against the logic elementseat 818 and stop flow to or from Port B.

The valve 800 provides a load sense port with a reverse flow check ball806 from Port C. The load sense check ball 806 is movably arranged withthe load sense port C such that the load sense check ball 806substantially prevents the flow of fluid into the load sense passageway920 through the load sense port C but allows the flow of fluid from theload sense passageway 920 out of the load sense port C.

In embodiments, Port A is a drain of the logic element spring chamber898 to the system reservoir. In yet other embodiments, Port A couldreceive a pilot signal that would allow the pressure setting of thelogic element to be variable.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A hydraulic suspension system comprising: acontroller; a pump adapted to provide a source of pressurized fluid anda tank adapted to hold a reservoir of fluid, the tank in fluidcommunication with the pump; a suspension cylinder in selective fluidcommunication with the pump, the suspension cylinder defining a chambertherein adapted to receive pressurized fluid; a proportionalpressure-reducing/-relief control valve interposed between the pump andthe suspension cylinder and between the suspension cylinder and thetank, the control valve in electrical communication with the controllerand in selective fluid communication with the pump, the tank, and thesuspension cylinder, the control valve including a spool reciprocallymovable over a range of travel between at least a pump flow position inwhich the pump and a control port of the control valve are in fluidcommunication with each other and a tank flow position in which the tankand the control port of the control valve are in fluid communicationwith each other, the control valve adapted such that the spool moves inresponse to a control signal received from the controller; a logicelement interposed between the control valve and the suspensioncylinder, the logic element in fluid communication with the controlvalve and in selective fluid communication with the suspension cylinder,the logic element including a poppet selectively movable between athrough-flow position in which fluid can flow in either directionbetween the chamber of the suspension cylinder and the control port ofthe control valve and a blocked position in which fluid is preventedfrom flowing out of the chamber of the suspension cylinder, the poppetbiased to the blocking position, the poppet adapted to move from theblocking position to the through-flow position when a pressure at afluid region upstream of the poppet exceeds a predetermined crackpressure, the fluid region upstream of the logic element poppet being influid communication with the control port of the control valve.
 2. Thehydraulic suspension system according to claim 1, wherein the logicelement comprises a piloted logic element including a pilot port, thepoppet of the logic element adapted to move from the blocking positionto the through-flow position when a pressure at the pilot port exceedsthe predetermined crack pressure, and the pilot port being in fluidcommunication with the control port of the control valve.
 3. Thehydraulic suspension system according to claim 2, wherein thepressure-reducing/-relieving control valve and the logic element areadapted such that, if the pressure controlled with thepressure-reducing/-relieving control valve is higher than the crackpressure of the logic element but lower than the pressure in the chamberof the suspension cylinder, the poppet of the logic element is in thethrough-flow position and fluid in the chamber of the suspensioncylinder drains therefrom, and if the pressure controlled with thepressure-reducing/relieving valve is higher than the crack pressure ofthe logic element and the pressure in chamber of the suspensioncylinder, the poppet of the logic element is in the through-flowposition and pressurized fluid flows from the pump to the chamber of thesuspension cylinder.
 4. The hydraulic suspension system according toclaim 2, wherein the controller is configured such that, once thecontroller receives a signal indicating that the suspension cylinderreaches a reference position or a reference pressure, the controller isadapted to control the control valve such that the spool of the controlvalve is disposed in the tank flow position such that the pressure atthe pilot port of the logic element falls below the crack pressure,thereby moving the poppet of the logic element to the blocked positionto maintain the suspension cylinder in the reference position or thereference pressure.
 5. The hydraulic suspension system according toclaim 2, further comprising: a load sense line in fluid communicationwith the control port of the pressure-reducing/-relieving control valve,the pilot port of the logic element, and a load sense port of the pump,the load sense line including a check valve adapted to prevent a flow offluid from the pump to the control valve or the logic element but toallow a flow of fluid to the pump, the load sense line adapted toprovide a load sense signal to the pump, the pump adapted to vary a flowof pressurized fluid in response to the load sense signal to generate adesired flow.
 6. The hydraulic suspension system according to claim 2,further comprising: an orifice disposed between the logic element andthe chamber of the suspension cylinder.
 7. The hydraulic suspensionsystem according to claim 6, wherein the orifice is adapted to control arate of flow of pressurized fluid to and from the chamber of thesuspension cylinder.
 8. The hydraulic suspension system according toclaim 2, farther comprising: a one-way restrictor disposed between thelogic element and the chamber of the suspension cylinder.
 9. Thehydraulic suspension system according to claim 8, wherein the one-wayrestrictor is adapted to control a rate of flow of pressurized fluidfrom the chamber of the suspension cylinder.
 10. The hydraulicsuspension system according to claim 2, further comprising: anaccumulator in fluid communication with and interposed between the logicelement and the chamber of the suspension cylinder.
 11. The hydraulicsuspension system according to claim 10, further comprising: a reliefvalve in fluid communication with the tank and in parallel fluidrelationship with the suspension cylinder, the accumulator, and thelogic element and adapted such that a pressurized fluid exceeding apredetermined threshold is diverted away from the accumulator and thesuspension cylinder to the tank.
 12. The hydraulic suspension systemaccording to claim 2, further comprising: a relief valve in fluidcommunication with the tank and in parallel fluid relationship with thesuspension cylinder and the logic element and adapted such that apressurized fluid exceeding a predetermined threshold is diverted awayfrom the suspension cylinder to the tank.
 13. The hydraulic suspensionsystem according to claim 2, wherein the proportionalpressure-reducing/-relief valve and the logic element are combined in asingle control valve.
 14. The hydraulic suspension system according toclaim 13, wherein the single control valve also includes a load sensecheck ball.
 15. The hydraulic suspension system according to claim 2,wherein the suspension cylinder includes a body and a piston assemblydisposed within the body and being reciprocally movable over a range oftravel between a retracted position and an extended position, the pistonassembly including a piston and a rod, at least a portion of whichextends from the body, the body defining a piston-side chamber and arod-side chamber, the chamber of the suspension cylinder comprising thepiston-side chamber, and further comprising: a second proportionalpressure-reducing/-relief control valve interposed between the pump andthe suspension cylinder and between the suspension cylinder and thetank, the second control valve in electrical communication with thecontroller and in selective fluid communication with the pump, the tank,and the suspension cylinder, the second control valve including a spoolreciprocally movable over a range of travel between at least a pump flowposition in which the pump and a control port of the control valve arein fluid communication with each other and a tank flow position in whichthe tank and the control port of the control valve are in fluidcommunication with each other, the control valve adapted such that thespool moves in response to a control signal received from thecontroller; a second piloted logic element interposed between thecontrol valve and the rod-side chamber of the suspension cylinder, thesecond logic element in fluid communication with the control valve andin selective fluid communication with the rod-side chamber of thesuspension cylinder, the second logic element including a pilot port anda poppet selectively movable between a through-flow position in whichfluid can flow in either direction between the rod-side chamber of thesuspension cylinder and the control port of the second control valve anda blocked position in which fluid is prevented from flowing out of therod-side chamber of the suspension cylinder chamber, the poppet of thesecond logic element biased to the blocking position, the poppet of thesecond logic element adapted to move from the blocking position to thethrough-flow position when a pressure at the pilot port of the secondlogic element exceeds a predetermined crack pressure, the pilot portbeing in fluid communication with the control port of the second controlvalve.
 16. The hydraulic suspension system according to claim 15,further comprising: a first accumulator in fluid communication with andinterposed between the first piloted logic element and the piston-sidechamber of the suspension cylinder; a second accumulator in fluidcommunication with and interposed between the second piloted logicelement and the rod-side chamber of the suspension cylinder.
 17. Thehydraulic suspension system according to claim 15, wherein thecontroller is configured such that, once the controller receives asignal indicating that the suspension cylinder reaches a referenceposition or a reference pressure, the controller is adapted to controlthe first pressure-reducing/-relieving control valve such that the spoolof the first control valve is disposed in the tank flow position suchthat the pressure at the pilot port of the first piloted logic elementfails below the crack pressure, thereby moving the first piloted logicelement to the blocked position to maintain the suspension cylinder inthe reference position or the reference pressure.
 18. The hydraulicsuspension system according to claim 1, wherein the controller isadapted to control the pressure in, or position of, the suspensioncylinder by transmitting the control signal to the proportionalpressure-reducing/-relief control valve in a cyclic on-off fashionwhereby adjusting the amount of time the control signal is on or off fora given time period correspondingly adjusts the pressure or position ofthe suspension cylinder.